In general, a thermoelectric device forms a PN junction pair by joining a P-type thermoelectric semiconductor and an N-type thermoelectric semiconductor via a metal electrode. It provides a temperature difference in the PN junction pair to generate electric power based on the Seebeck effect, so that it can function as an electrical generator. In addition, it can be also utilized as a temperature controller using the so-called Peltier effect, where one of the junction portions is cooled and the other thereof is heated by applying current to the device.
In general, the thermoelectric device is utilized by being incorporated in a thermomodule in which dozens to several hundreds of PN junction pairs (thermoelectric devices) are formed in series. The thermoelectric device used for the thermomodule maintains the shape as a structural body and is constructed of: two boards having metal electrodes to form a PN junction pair, a plurality of P-type and N-type thermoelectric semiconductors sandwiched between these boards, and a junction material for making a junction between the P-type and N-type elements and the metal electrodes.
Here, the P-type and N-type thermoelectric semiconductor materials include Bi—Te type materials, Fe—Si type materials, Si—Ge type materials, and Co—Sb type materials. Among them, in particular, the Bi—Te type materials are preferably used.
As described above, the thermoelectric device is provided as a n-type (pie type) device by connecting two different thermoelectric semiconductors, P-type and N-types. A number of such devices are connected in series to form an assembly of thermoelectric devices, thereby constructing a thermoelectric module. A Bi2Te3 based material has been mainly used as a material for the thermoelectric device as described above. However, it is considered to lead high material costs, lack of stability at high temperature, poor workability, and high environmental load. In addition, when the PN junction is formed via a lead plate, the contact resistance with the lead plate increases, so that the original capability of the material itself may not be fully achieved. On the other hand, a metal-based material, which is cheap and excellent in contact resistance, has a small Seebeck coefficient. Thus, it is particularly preferable that a sufficient electric power can be obtained when a lot of PN junction pairs are connected to each other in series.
These multiple PN junction pairs connected in series are, for example, a plurality of n-type elements arranged between two boards (Patent Document 1).    Patent Document 1: Japanese Unexamined Patent Application Publication No. Hei 11-251649 (FIG. 1)